1. Field of the Invention
The present invention relates to a DNA vaccine comprising a DNA construct. The present invention also relates to a pharmaceutical composition and a method of generating said DNA vaccine.
2. Description of the Related Art
Cervical cancer is a main cause of death in women, and persistent infection with known high-risk Human papillomavirus (HPV) types, such as HPV subtype 16 (HPV-16) is directly linked to development and progression of cervical cancer. Although the present HPV vaccines can be used to prevent cervical cancer, it is not yet known whether they are useful for treating HPV-associated cervical cancer or ameliorating the existing HPV infection or HPV-associated lesions. Therefore, it is advantageous to develop a safe and effective therapeutic vaccine for treatment of HPV-associated cervical cancer, HPV-associated other genital cancers (e.g., vaginal, vulvar, penile) and other HPV-associated lesions of head and neck, and gastrointestinal system, as well as for the treatment of precancerous lesions of the same areas.
In recent years, DNA vaccines have been developed and evaluated in a variety of disease models as promising therapeutic agents for treating a variety of diseases including their use as immunotherapy in certain cancers. Therapeutic DNA vaccines are introduced into antigen-presenting cells (APCs) of the recipient's immune system to express a protein antigen, the protein antigen is processed and presented by the major histocompatibility antigen (MHC) class I and II molecules to induce immune responses, such as helper T-cell response, cytotoxic T-cell response and humoral (antibody) response, and a direct result is that tumor cells expressing said antigen can be eliminated by the immune system.
In comparison with “traditional” (protein antigen) vaccines, DNA vaccines have many advantages such as high specificity, safety, stability, cost-effectiveness, and the ability to induce several types of immune responses. DNA vaccines do not pose any risk of infection because only certain sequences of the pathogen's DNA is used in their manufacture, in contrast to “live” and “attenuated” vaccines. Also, no toxic adjuvants are needed for practical use of DNA vaccines. DNA vaccines are also easier to prepare than “subunit” vaccines because no protein antigens need to be expressed and purified prior to injection into the patient.
However, because the lifespan of APCs is limited, the efficacy of DNA vaccines is limited because APCs are not able to process and present the antigen indefinitely. Therefore, several strategies have been applied to increase the potency of DNA vaccines, such as targeting an antigen by fusing molecules to enhance antigen processing (Cheng et al., 2001; Chen et al., 2000), targeting antigens for rapid intracellular degradation (Rodriguez et al., 1997), directing antigens to APCs by fusion to ligands for APC receptors (Boyle et al., 1998) or to a pathogen sequence such as fragment C of tetanus toxin (King et al., 1998), co-injecting cytokines (Weiss et al., 1998), and administering with CpG oligonucleotides (Klinman et al., 1997).
Combined strategies for enhancing the effects of DNA vaccines have been introduced in the development of cancer vaccines and immunotherapy, and overexpression of an anti-apoptotic molecule is a potential strategy for overcoming the short lifespan of APCs. For example, the administration of a DNA vaccine which comprises fragments encoding an antigen and an inhibitor of apoptosis of dendritic cells (DCs) can prolong the survival of DCs, thereby enhancing the potency of the DNA vaccine (Kim et al., 2003). Other research has demonstrated that combining a tumor antigen and an apoptosis inhibitor, such as Bcl-X1, Bcl-2, XIAP, dominant negative caspase-9, or dominant negative caspase-8, can enhance the antigen-specific immunity and the anti-tumor effects (Kim et al., 2003; Kim et al., 2004; Kim et al., 2005). Thus, DC-based vaccination could be enhanced by an approach that inhibits apoptosis and prolongs the survival of antigen-expressing DCs in vivo. However, some apoptosis inhibitors, such as proteins of Bcl-2 family, are known to be over-expressed in some cancers and therefore they are implicated in contributing to cellular immortalization. This safety issue cannot be ignored.